Last week we began discussing the many different problems which are common in roses and are caused by insects. We discussed how to diagnose and treat insect problems such as beetles, rose midge, leaf cutter bees, rose cane borers, aphids, thrips, leaf rollers and spider mites.
Roses Disease and how to treat those problems
This week we are going to address several more common problems which may be affecting your roses, such as disease and how to treat those problems.
Symptom: Tumor-like growths on canes, roots, or at the bud union.
Cause: Gall (aerial, crown or root)—This is a bacterial pathogen that enters through a wound on your rose plant or by a pruning tool that is contaminated.
Treatment: Prune away any sections which are infected if possible. Sterilize your pruning shears and other hand tools with bleach or alcohol to prevent the bacteria from spreading. Any plants which are seriously weakened should be destroyed. You will need to treat the soil with a bactericide or leave it fallow for two seasons before you replant.
Symptom: White powdery material appears on young growth.
Cause: Powdery Mildew—This is a fungal disease that is fostered by warm days and cool nights.
Treatment: At first you should try spraying the affected areas with a solution of baking soda and dish soap. Make sure that the plants have good air circulation and an ample amount of sunlight. If you need to treat your roses further, then you will need to treat them with a fungicidal product for powdery mildew control.
Symptom: Dark, irregular splotches on foliage, dropping of apparently healthy leaves, sections of yellow leaves.
Cause: Downy Mildew—This is a fungal disease that may appear when nights are cool and humid. This mildew can develop very rapidly.
Treatment: Water your rose plants early in the day to allow the surface of them to dry thoroughly. Avoid overhead irrigation and prevent water from collecting around the plants. Cut the defoliated plant back. Clean up any debris and then dust with sulfur. Then spray the roses with a fungicide that lists downy mildew as a target.